• Tribology and Lubricants
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• 제24권4호
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• pp.163-169
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• 2008

Tribological properties of ceramic brake discs were investigated using a commercial friction material. The discs were manufactured by liquid silicon infiltration (LSI) into a C-C preform. The disc surface was modified by two different methods, producing sliding surfaces with chopped carbon fibers and carbon felt. In addition, the composition of the surface was also changed. Friction characteristics of the discs were examined using a 1/5 scale dynamometer. Results showed that the type and composition of the disc surface significantly affected the level of braking effectiveness and high temperature brake performance. The discs with felt surfaces showed higher friction levels than those with chopped fiber surfaces and SiC tended to increase the friction level while C lowered the friction coefficient. The ceramic disc was more sensitive to the deceleration rate than gray iron, showing high speed sensitivity.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 춘계학술대회 논문집
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• pp.20-23
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• 2001

Hypereutectic Al-25Si alloy, which is expected to be applied to the cylinder-liner-part of the engine-block of an automobile due to its excellent wear resistance, low density and low thermal expansion coefficient, has been fabricated through a spray forming process. The obtained microstructure of the hypereutectic Al-25Si alloy appeared to consist of Al matrix and equiaxed Si particles of average diameter of 5-7 mm. To characterize the deformation behavior of this alloy, a series of load relaxation and compression tests have been conducted at temperatures ranging from RT to $500^{\circ}C$. The strain rate sensitivity parameter (m) of this alloy has been found to be very low (0.1) below $400^{\circ}C$ and reached maximum value of about 0.2 at $500^{\circ}C$. During the deformation above $300^{\circ}C$ in compression, strain softening has been observed. The diagram of extrusion pressure vs. ram-speed has been constructed. The extrusion has been successfully conducted at the temperatures of $300^{\circ}C$ and above with the ratio of area reduction of 28 and 40 in this study.

• Structural Engineering and Mechanics
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• 제53권5호
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• pp.867-880
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• 2015

Mechanical fastening is still one of the main methods used for joining components. Different techniques have been applied to reduce the effect of stress concentration of notches like fastener holes. In this work we evaluate the feasibility of combining laser shock peening (LSP) and cold expansion to improve fatigue crack initiation and propagation of open hole specimens made of 6061-T6 aluminum alloy. LSP is a new and competitive technique for strengthening metals, and like cold expansion, induces a compressive residual stress field that improves fatigue, wear and corrosion resistance. For LSP treatment, a Q-switched Nd:YAG laser with infrared radiation was used. Residual stress distribution as a function of depth was determined by the contour method. Compact tension specimens with a hole at the notch tip were subjected to LSP process and cold expansion and then tested under cyclic loading with R=0.1 generating fatigue cracks on the hole surface. Fatigue crack initiation and growth is analyzed and associated with the residual stress distribution generated by both treatments. It is observed that both methods are complementary; cold expansion increases fatigue crack initiation life, while LSP reduces fatigue crack growth rate.

• 대한조선학회논문집
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• 제33권2호
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• pp.96-110
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• 1996

노후선박은 부식, 피로균열 등의 구조손상을 입고 있으며, 구조손상이 심각하면 중대한 해난사고를 초래할 위험성이 높다. 선각붕괴에 의한 선박의 침몰사고를 미연에 방지하기 위하여는 구조손상에 기인된 각종 불확실성을 고려한 노후선박의 최종강도 신뢰성을 평가할 필요가 있다. 본 논문에서는 부식에 의한 선체구조부재의 판두께 감소효과를 고려하여 선체구조의 최종강도를 기준으로한 신뢰성 평가기법을 제시하였다. 이를 위해 선체구조의 부식 속도모델을 선급에서 제시하는 데이타를 바탕으로 설정하고, 부식효과를 고려한 신뢰성 한계상태방정식을 도출하였으며, 최종강도 신뢰성은 SORM (second-order reliability method)을 적용하여 계산하였다. 본 기법을 이중선체 유조선에 적용하여 선령의 증가에 따른 단면계수 및 최종강도 신뢰성의 감소특성을 고찰하였다.

• 상하수도학회지
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• 제31권6호
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• pp.521-527
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• 2017

Phosphorus is one of the limiting nutrients for the growth of phytoplankton and algae and is therefore one of leading causes of eutrophication. Most phosphorous in water is present in the form of phosphates. Different technologies have been applied for phosphate removal from wastewater, such as physical, chemical precipitation by using ferric, calcium or aluminum salts, biological, and adsorption. Adsorption is one of efficient method to remove phosphates in wastewater. To find the optimal media for phosphate removal, physical characteristics of media was analysed, and the phosphate removal efficiency of media (silica sand, slag, zeolite, activated carbon) was also investigated in this study. Silica sand showed highest relative density and wear rate, and phosphate removal efficiency. Silica sand removed about 36% of phosphate. To improve the phosphate removal efficiency of silica sand, Fe coating was conducted. Fe coated silica sand showed 3 times higher removal efficiency than non-coated one.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.1004-1007
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• 2001

This paper presents the experimental results to verify the environmental consciousness with economic balances due to cutting fluid behaviors, effectiveness in machining process. Even though cutting fluid improves the machined part quality through the cooling and lubracating effects, its environmental impact is also increased according to the cutting fluid usage. Because cutting fluid are used by experience than science on shop floors, its environmental impact are more serious to human health hazard, shop floor environments. In this study a few cutting parameters are adopted as the machinability index (i.e. ; tool wear and surface roughness), and aerosol mist diffusion rate of cutting fluid as the environment consciousness index. These indeces are analyzed quantitatively via a few experiements. The results of this study can be facilitate the optimization of cutting fluid usage in achieving a balanced environmental consciousness consideration with economic view.

• 대한가정학회지
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• 제19권3호
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• pp.33-40
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• 1981

The purpose of this research was to see through the special qualities and prospects I different localities as to compare the actual conditions of clothes for everyday wear of the city with the town. The results investigated the style of dress in Deajeon city and youseong town throughout Winter, Spring, and Summer were as follows: 1) In hair style, commonly throughout Winter, Spring, summer, permanent style was superior in number as compared with the chignon In youseong, throughout Winter and Spring, chignon far out-numbered permanent one. 2) In winter, while citizens wore more half coats than long ones, the townsfolk had long coats on as many as that. In Spring and Summer, people dressed in blouse were shown aplenty both Deajeon and youseong and it was the latter that became more and more conspicuous I Summer. The degrees of wearing korean clothing were shown at a high rate in youseong I Spring. In both regions, throughout the year, adjusting themselves forward was of frequent occurrence. 3) In Winter and Spring, both of them put long skirts on and in Summer put normal skirts to frequent use respectively. jean pants were shown in Daejeon remarkable in spring, while the townsfolk wore Mon-pae and korean clothing. 4) throughout Spring and Summer, slippers were frequent use commonly in both regions. And in Spring, people put on more Ko Mu, sin than shoes, especially in youseong. The downward-phase shoestype has been shown markedly in both regions but Daejeon has shown a sharp contrast to youseong.

• 대한간호학회지
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• 제34권8호
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• pp.1477-1482
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• 2004

Purpose. With the continuous spread of the AIDS virus and other sexually transmitted diseases (STDs) throughout Asia, it has become imperative for HIV/AIDS prevention outreach programs to stress the need for using prophylactics as one form of protection. This is particularly true for commercial sex workers. This pilot study was conducted to investigate the rate of condom use among the commercial sex workers in Korea and reasons why they frequently do not wear condoms during sexual intercourse. Methods. Fifty female commercial sex workers who worked in the Yong San area were recruited while outreach was performed and forty eight responses were analyzed due to two incomplete questionnaires. The data were collected on June 28, 2004 as part of an outreach program for condom use promotion. Results. The subjects ranged in age from 21 to 45 years. Nearly half of the subjects ($47.9\%$) did not consistently use condoms. The major reason for not using protection was clients' reluctances for using condoms. When condoms were used, the subjects preferred lubricant-rich and less painful condom during intercourse. Conclusion. Due to the inconsistent use of condoms, it is clear that many commercial sex workers and clients are susceptible to sexually transmitted diseases. Therefore, it is important to not only educate commercial sex workers, but also to educate their pimps and clientele about the importance of condom use. In general, it is recommended that practical strategies and a policy for condom use promotion be developed.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.858-861
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• 2000

This paper presents the characteristics of cutting fluid atomization due to its application method. In this study three different application methods; nozzle, jet, mist type is adopted for evaluating the cutting fluid's effect in terms of machinability and environmental consciousness. Cutting fluids are widely used to cool and lubricate the cutting zone in machining process. Cutting fluids mist via atomization in spin-off process can be affected to health risk. To satisfy the increasing concern of health and environment problem and keep the machinability or productivity it is necessary to establish the resonable strategy of cutting fluid usage and optimal control. Tool wear and cutting fluid diffusion rate in the air were measured as machinability index and environmental index in a few turing operation. Through this basic approach it can be also provide the optimization of cutting process and improvement of machine tool design in achieving environmentally conscious machining.

• 한국기계가공학회지
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• 제7권2호
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• pp.23-30
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• 2008

As a basic machining process, turning is a widely used machining process in which a single-point cutting tool removes material from the surface of a rotating material. A common method of evaluating machining performance is to measure the surface roughness. In a turning operation, it is important to select cutting conditions for achieving high cutting performance. As a rule, cutting conditions can be classified into feed rate, depth of cut and insert radius. While cutting process even though cutting conditions are optimized, the average roughness can be deterioration due to wear of the cutting tool edge. In this study, the aim is to maintain the average roughness even though the cutting condition is irregularly changing within the predictable range due to the working environment. First, the surface roughness model influenced by cutting conditions is constructed based on the experimental results in a turning operation, Second, applying the sliding mode control theory to the turning operation model which is composed of the surface roughness model and the motor transfer function, the surface roughness is closed to the desired value. Finally, the effectiveness of this approach is demonstrated through the computer simulation.